Many years ago, I had the idea of using Ruby as a configuration language. It lends itself nicely to representing tree structures and has some convenient featur

Many years ago, I had the idea of using Ruby as a configuration language. It lends itself nicely to representing tree structures and has some convenient features like ranges. It all worked well as long as we stuck to the subset of Ruby I intended. One day one of the other developers introduced a change to the configuration that had a side effect. It made sense; after all, the configuration is read at startup, so surely it makes sense to put code there that you want to have run at startup? You can imagine my surprise when I made change that read the configuration again after startup. Configuration should be purely functional and idempotent, with no side effects, or as you say, inert.